1. Field of the Invention
The present invention relates to a rotary compressor for use in a refrigerating apparatus.
2. Description of the Prior Art
In prior refrigerating apparatus, it is common for a high temperature and high pressure gas in a closed casing of a compressor to flow into an evaporator which is maintained at a low pressure in a refrigerating system when the operation of a rotary compressor is suspended, thereby increasing the heat load on the refrigerating apparatus. Therefore, Japanese Patent Application No. 86447/1981 has proposed a rotary compressor which incorporates a valve mechanism for cutting off flow of low-pressure and high-pressure gas and designed to open during the operation of the rotary compressor and close during the suspension of the rotary compressor, thereby attaining reduction in the heat loss generated during the suspension of the rotary compressor.
In a rotary compressor of the invention of the above-mentioned application, a slide valve acting as a valve for cutting off flow of high-pressure gas is provided at a portion of a cylinder plate which constitutes a compression element of the rotary compressor, and an inlet port adapted to be opened and closed by means of a piston-like slider is connected at its one end to a closed casing and an outlet port is connected to a discharge pipe which extends through the closed casing. The rotary compressor of this type also includes a reed valve type check valve which serves as a valve for cutting off flow of low-pressure gas, and is disposed between a suction pipe and a cylinder. In the thus-arranged rotary compressor, the high-pressure and low-pressure gas cut-off valves are both closed when the operation of the compressor is suspended, so that the high-temperature and high-pressure gas in the closed casing is prevented from flowing into the evaporator through the condenser to cause any increase in the heat load of the refrigerating apparatus. As the compressor is operated, pressure difference between the closed casing and the cylinder actuates the slider to communicate the inlet port with the outlet port, and to open the high pressure cut-off valve, thereby feeding pressurized gases to the condenser. The low-pressure gas cut-off valve is open by this time to afford a normal cooling operation.
The rotary compressors of the prior art suffer from a problem in that since the high-pressure gas cut-off valve is of a slide valve type, there is a limit to its anti-leakage performance when closed. In order to attain an improved anti-leakage performance, the clearance between the slide valve and a valve cylinder in which the slide valve moves must be maintained at a minimal value. However, this requires improved work accuracy and increases the cost of machining and assembly work such as matching assembly.
Further, foreign matters such as abrasion powder generated by the rotating and sliding portions of the rotary compressor during its operation may enter the clearance, generating an hydraulic lock which may lead to disabled operation of the rotary compressor.
In case an effettive pressure surface of a spool valve is increased so as to reduce the pressure difference required at the time of starting, a larger space is required to enable mounting a high-pressure gas cut-off valve, and noise may be generated during the operation due to the increased weight of the rotary compressor.